Inappropriate use of antibiotics has been well documented for inpatient settings, but there are few studies in ambulatory patients. In a prospective study, the authors monitored the outpatient prescribing patterns of internal medicine residents and evaluated the effect of placing a one-page set of antibiotic guidelines in each patient examining room. Appropriateness of antibiotic choices was scored periodically. A 12-month pre-intervention survey of antibiotic use showed that 50% of the choices were inappropriate. Comparison of a four-month post-intervention analysis with the same four-month interval in the pre-intervention period showed no significant difference between the percentages of inappropriate prescriptions. The most common reasons for inappropriate use were: 1) failure to document a clinically significant bronchial infection, and 2) inadequate evaluation of nonspecific urinary tract complaints. The authors conclude that the ready availability of information about appropriate antibiotic use is not effective in changing antibiotic choices, and that educational strategies regarding antibiotic use must also address diagnostic evaluation.